front sight

Hey guys, pardon if I have the wrong nomenclature, but on my front night sight the tritium is still there, but it had a bright yellow ring around it, and it fell out and I can't find it. Anyone heard of this before? It's not the stock green circle/ring, but an aftermarket bright yellow ring...

I'm taking my 13 year old, ballerina daughter to Front Sight for Spring Break. She's strong but only as big around as a twig. I want her to get as much from the class as she can and not worrying about being beat up by the gun. I'm thinking of having her shoot my 23 with an Advantage Arms 22...